Orbital densifier



Nov. 30, 1965 G. E. GARD ORBITAL DENSIFIER Filed March 16, 1964 FIGI INVENTOR GEORGE E- GARD ATTORNEY United States Patent 3,220,705 ORBITAL DENSIFIER George E. Gard, East Hernpfield Township, Lancaster, County, Pa., assiguor to Armstrong Cork Company, Lancaster, Pa., a corporation of Pennsylvania Filed Mar. 16, 1964, Ser. No. 352,238 3 Claims. (Cl. 259129) This invention relates generally to a device for smoothing out density variations in a loosely packed mass of lightweight, cellular particles in a size range of about inch to about inch. More particularly, the invention relates to apparatus for increasing the bulk density of a mass of loosely packed cellular particles having metallic slivers intermixed therewith, the mixture constituting an artificial dielectric from which may be molded Lunebergtype lens elements.

Luneberg-type lenses have the ability to focus microwave radiation. One of the methods of causing the focusing of such radiation is to fabricate a lens of generally constant density but having distributed throughout a variable number of tiny metallic slivers. The manufacture of lens elements from which the completed lens may be assembled has presented a problem in maintaining the requisite anisotropy both as to orientation and concentration of the metallic slivers and as to density variations in the cellular material itself. Cellular particles having the requisite concentration of metallic slivers admixed therewith are, in one method of manufacturing lens elements, placed in a charging box measuring approximately 2 feet square. The charge is subsequently transferred to a mold where it is treated with heat and pressure to form a low-density block having the requisite electrical characteristics for assembly into a completed lens.

However, the handling of the cellular particles and the slivers gives rise to certain sliver orientation and to certain density variations which tend to destroy the requisite anisotropy. Accordingly, there has been a need for a means or device to increase the bulk density of the particlesliver mixture while maintaining random sliver orientation, all to the end that the finished molded block will be suitable for use for the purpose intended.

It is the primary object of the present invention to supply such a device. It is a further object of the present invention to supply a densifying device which is simple of operation and inexpensive of construction, and which will not increase processing time in the manufacture of lens elements.

These objects are accomplished in a straightforward and effective manner. The invention contemplates an apparatus comprising a first grate having openings therein formed by the intersection of the grate bar members, the openings being in a size range of three to ten times the size of the cellular particles to be densified. Mounted on the first grate is a first array of pegs extending in an upwardly direction. Cooperating with the first grate is a second grate having openings therein of the same size as the openings in the first grate and supporting a second array of pegs mounted on the second grate and extending in a downwardly direction parallel to the pegs in the first array. The two grates are parallel and are spaced apart a distance the length of the pegs. Finally, the invention includes a means for rotating one array of pegs with respect to the other array of pegs while maintaining the two grates parallel.

The invention will be better understood by reference to the attached drawings in which,

FIG. 1 is an isometric view of the orbital densifier of the present invention, and

FIG. 2 shows the orbital densifier mounted in position above the charging box.

Patented Nov. 30, 1965 Referring to FIG. 1, grate bar members 1 intersect to form openings 2. Upwardly extending pegs 3 are mounted on the intersection of the grate bar members 1. The upwardly extending pegs 3 could be mounted at any convenient point on the grate bar members 1, but greater strength is achieved at the intersections of the grate bar members. The grate bar members may be soldered, welded, brazed, or otherwise aflixed to each other to form the lower grate which serves to support the upwardly extending pegs 3.

The second grate bar members 4 form a second grate having openings 5, the second grate being in position generally parallel to the first grate. The downwardly extending pegs 6 are afiixed to the second grate. The pegs 3 and pegs 6 are of the same length, and the two grates are positioned apart a distance approximately equal to-this length. Rotating means 7 rotates the upper grate and the pegs 6 mounted thereon to impart an orbital or rotary motion to the pegs 6 while the two grates are parallel to each other and at a distance apart equal to the length of the two sets of pegs 3 and 6. The lower grate is maintained in a fixed position. It will be appreciated that the rotating means 7 may be mounted to the lower grate while the upper grate is held motionless. The rotating means 7 as shown is driven by a rotating pulley 8 driven by a belt 9 connected to a suitable motor, not shown.

The rate of rotation of one set of pegs with respect to another may vary considerably. Five to 40 rpm. may be used, with 10 rpm. a good working average. The peg length will generally vary in the range of 2-6 inches, with 3 /24 inches being a good workable average. The pegs themselves are made of rods of metal which will not bend or change shape during operation, with the diameter being in the range of inch to 7 inch. Since the cellular particles and the metallic slivers must fall through both grates during operation, the grate openings 2 and 5 will generally be in a size range of three to ten times the size of the cellular particles which themselves will be in a size range of about inch to inch. These particles will usually be cellular polystryrene containing small amounts of a blowing agent, most often a low-boiling liquid hydrocarbon such as petroleum ether. Hence particles and slivers will flow readily through the openings in both grates. The pegs will generally be positioned apart a distance approximately equal to the size of the openings in the grates.

The operation of the orbital device in the over-all process is shown in greater detail in FIG. 2. In FIG. 2, the charge box 10 has a movable bottom 11 which is positioned at the start of the filling operation immediately beneath the orbital densifier 12 of the present invention. A stream, not shown, of artificial dielectric media 13 comprising a mixture of cellular particles and metallic slivers is fed from a suitable blending operation, not shown, to the loading chute 14 positioned above the orbital densifier 12. The artificial dielectric media will come to rest on the movable bottom 11 and Will soon have submerged and buried the orbital densifier 12. The upper grate of the orbital densifier 12 will have been rotating from the beginning of the operation. As the depth of the artificial dielectric media 13 becomes suflicient to reach the upper grate of the orbital densifier 12, the movable bottom 11 of the charge box 10 will be lowered at a rate commensurate with the incoming stream of artificial dielectric media to maintain the level in the charge box 10 approximately even with that of the upper grate. Thus the movable bottom 11 slowly falls, the orbital densifier 12 functions to density the mass of particles and slivers passing through it, until the movable bottom 11 reaches the bottom of the charge box 10 at which point the operation ceases. The charge box 10 may then be physically transferred to a mold in which the solid unified monolithic block is to be prepared by subjecting the cellular particles to heat and pressure.

It has been found that use of the orbital densifier of the present invention increases the bulk density of the mass of particles and sliversin the charge box by as much as 10%. Additionally, density variations are smoothed out. Handling of the particles subsequent to filling of the charge box does not produce undesirable isotropy either as to density variations or as to sliver orientation.

Additional improvement in anisotropy may be obtained by rotating the charge box 10 during the leading operation while the orbital densifier 12 is working. The tighter pack of the particles and the increased bulk density achieved prevent metallic sliver migration during the subsequent handling and molding operation.

I claim:

1. Apparatus for increasing the bulk density of a loosely-packed mass of individual cellular particles in a size range of about /3 inch to /1 inch, said apparatus comprising a first grate having openings therein formed by the intersection of the grate bar members, said openings being in a size range of three to ten times the size of said particles, a first array of pegs mounted on said grate and extending in an'upwardly direction, a second grate having openings therein of the same size of the openings in the first grate, a second array of pegs mounted on said second grate and extending in a downwardly direction parallel to the pegs in said first array, said two grates being parallel and spaced apart a distance the length of said pegs, and means for rotating one array of pegs with respect to the other array of pegs while maintaining said two grates parallel.

2. Apparatus according to claim 1 in which said openings are square in shape.

3. Apparatus according to claim 1 in which all of said pegs have a length in the range 3 /24 inches.

No references citedv WALTER A. SCHEEL, Primary Examiner. 

1. APPARATUS FOR INCREASING THE BULK DENSITY OF A LOOSELY-PACKED MASS OF INDIVIDUAL CELLULAR PARTICLES IN A SIZE RANGE OF ABOUT 1/8 INCH TO 3/4 INCH, SAID APPARATUS COMPRISING A FIRST GATE HAVING OPENINGS THEREIN FORMED BY THE INTERSECTION OF THE GRATE BAR MEMBERS, SAID OPENINGS BEING IN A SIZE RANGE OF THREE TO TEN TIMES THE SIZE OF SAID PARTICLES, A FIRST ARRAY OF PEGS MOUNTED GRATE AND EXTENDING IN AN UPWARDLY DIRECTION, A SECOND GRATE HAVING OPENINGS THEREIN OF THE SAME SIZE OF THE OPENINGS IN THE FIRST GRATE, A SECOND ARRAY OF PEGS MOUNTED ON SAID SECOND GRATE AND EXTENDING IN A DOWNWARDLY DIRECTION PARALLEL TO THE PEGS IN SAID FIRST ARRAY, SAID TWO GRATES BEING PARALLEL AND SPACED APART A DISTANCE THE LENGTH OF SAID PEGS, AND MEANS FOR ROTATING ONE ARRAY OF PEGS WITH RESPECT TO THE OTHER ARRAY OF PEGS WHILE MAINTAINING SAID TWO GRATES PARALLEL. 